1. Field of the Invention
The present invention relates generally to a marine outboard drive, and more particularly to a marine engine.
2. Description of Related Art
Many types of marine engines include an induction system which forms and delivers a fuel charge to the engine. Such induction systems commonly include at least one charge former (e.g., a carburetor) which communicates with an intake manifold that delivers the fuel charge to the internal combustion engine.
Such induction systems, however, tend to deliver inconsistent air/fuel mixtures (i.e., the ratio between air and fuel varies), especially when operated in cold weather. The fuel of the air/fuel mixture deposits on the cool inner surfaces of the intake manifold, thus altering the ratio of fuel to air within the fuel charge. Engine combustion consequently becomes inconsistent.
Engine combustion inconsistence also occurs in prior marine internal combustion engines because temperature differences exist between the upper and lower portions of the engine. Conventional water cooling systems of marine engines continuously draw water from the body of water in which the marine drive is operated and force the water up through the engine. The water flowing through the lower portion of the engine is cooler than the water flowing through the upper portion of the engine. The water thus absorbs more heat at the lower portion of the engine than at the upper portion and consequently a temperature difference occurs between the upper and lower portions of the engine.
This problem is particularly acute in outboard motors where the combustion chambers are positioned vertically above one another. The temperature of the lowermost cylinder commonly is less than the temperature of the uppermost cylinder as a result of the lower portion of the engine being cooler than the upper portion of the engine. The resulting temperature differential between cylinders affects the consistence of fuel combustion between cylinder.